segment routing lab
TRANSCRIPT
Segment Routing Lab Santiago Alvarez Maan Al Bachari Thierry Couture
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§ Please ensure your cellphones / laptops are set on silent to ensure no one is disturbed during the session
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House Keeping Notes
§ Source Routing: source chooses a path and encodes it in packet header as an ordered list of segments.
§ Segment: an identifier for any type of instruction § Service § Context § Locator § IGP-based forwarding construct § BGP-based forwarding construct § Local value or Global Index
Segment Routing Key Concepts
Segment = Instructions such as "go to node N using the shortest path"
§ MPLS: an ordered list of segments is represented as a stack of labels § SR re-uses MPLS data plane
without any change
§ IPv6: an ordered list of segments is represented as a routing extension header
Segment Routing
This lab focuses on MPLS data plane
IPv6 IPv6
IPv6
Control Plane
IPv4
MPLS Data Plane
§ Locally significant to node allocating it
§ Node processes SID and switches packet towards adjacency
§ Advertised as an absolute value
IGP Segment Identifiers
§ Globally significant within SR domain
§ All nodes switch packet towards prefix/node via shortest path
§ Advertised as a relative (index) value
§ Make use of a per-node reserved block (SR Global Block or SRGB)
B C
N O
Z
D
P
A
9101 9105
9107
9103
9105
B C
N O
Z
D
P
A
65
65
65 65
Prefix/Node SID Adjacency SID
MPLS Control and Forwarding Operation with Segment Routing
PE1 PE2
IGP PE1 PE2
Services
IPv4 IPv6 IPv4 VPN
IPv6 VPN VPWS VPLS
Packet Transport LDP
MPLS Forwarding
RSVP BGP Static IS-IS OSPF
No changes to control or forwarding plane
IGP label distribution for IPv4 and IPv6, same forwarding plane
BGP / LDP
§ Prefix SID § SID encoded as an index § Index represents an offset from SRGB base § Index globally unique § SRGB may vary across LSRs § SRGB (base and range) advertised with router
capabilities
§ Adjacency SID § SID encoded as absolute (i.e. not indexed)
value § Locally significant § Automatically allocated for each adjacency
SID Encoding
SRGB = [ 16000 - 23999 ]. Advertised as base = 16,000, range = 7999 Prefix SID = 16041. Advertised as Prefix SID Index = 41 Adjacency SID = 24000. Advertised as Adjacency SID = 24000
SR-enabled Node
§ Each pod has a dedicated test bed that has been partially pre-configured
§ The devices dedicated to a pod are isolated from the devices assigned to other pods
§ Follow the tasks and steps in the order provided
§ Explore the entire test bed and verify operation beyond the sample output provided
Lab General Instructions
Lab Testbed Topology
g0/0/0/1
g0/0/0/1
g0/0/0/0
g0/0/0/2
lo0
lo0
g0/0/0/0
lo0 lo0
IS-IS Area 49.0002
IS-IS Area 49.0001
P1 IS-IS L1-L2
P2 IS-IS L1-L2
PE1 IS-IS L1
PE2 IS-IS L2
P1 IS-IS L1-L2
P2 IS-IS L1-L2
PE1 IS-IS L1
PE2 IS-IS L2
192.168.255.2 /32 (VRF RED)
g0/0/0/0 172.16.1.0/31
Lab Testbed Topology (IPv4 Addressing)
g0/0/0/1 172.16.2.2/31
g0/0/0/1 172.16.1.2/31
g0/0/0/0 172.16.2.0/31
g0/0/0/2 172.16.2.4/31
lo0 172.16.255.1/32 lo0
172.16.255.2/32
172.16.255.101/32 lo0
lo0 172.16.255.102/32
.4
.5
.0
.1
.2
.3
.2
.3
.0
.1
IS-IS Area 49.0002
IS-IS Area 49.0001
2001:db8:a::ff:2 /128 (VRF GREEN)
192.168.255.1 /32 (VRF RED)
2001:db8:a::ff:1 /128 (VRF GREEN)
Lab Testbed Topology (IPv6 Addressing)
g0/0/0/0 2001:db8::1:0/127
g0/0/0/1 2001:db8::1:2/127
g0/0/0/2 2001:db8::2:4/127
Lo0 2001:db8::ff:1/128
2001:db8::ff:101/128 lo0
lo0 2001:db8::ff:102/128
:4
:5
:0
:1
:2
:3
:2
:3
:0
:1
g0/0/0/1 2001:db8::2:2/127
g0/0/0/0 2001:db8::2:0/127
IS-IS Area 49.0002
IS-IS Area 49.0001
lo0 2001:db8::ff:2/128
2001:db8:b::ff:2 /128 (Global)
2001:db8:b::f:1 /128 (Global)
P1 IS-IS L1-L2
P2 IS-IS L1-L2
PE1 IS-IS L1
PE2 IS-IS L2
§ When a node is LDP capable but its next-hop along the SPT to the destination is not LDP capable § no LDP outgoing label
§ In this case, the LDP LSP is connected to the prefix segment
§ C installs the following LDP-to-SR FIB entry: § incoming label: label bound by LDP for FEC Z § outgoing label: prefix segment bound to Z § outgoing interface: D
§ This entry is derived automatically at the routing layer
LDP/SR Interworking - LDP to SR
A
C B D
Z
16066
LDP SR
Input Label (LDP)
Out Label (SID), Interface
32 16066, 1
Prefix Out Label (LDP), Interface
Z 16, 0
§ When a node is SR capable but its next-hop along the SPT to the destination is not SR capable § no SR outgoing label available
§ In this case, the prefix segment is connected to the LDP LSP § Any node on the SR/LDP border
installs SR-to-LDP FIB entry(ies)
LDP/SR Interworking - SR to LDP
A
C B D
Z
16066
SR LDP
Input Label (SID)
Out Label (LDP), Interface
? 16, 1
Prefix Out Label (SID), Interface
Z ?, 0
§ A wants to send traffic to Z, but § Z is not SR-capable, Z does not advertise any prefix-
SID à which label does A have to use?
§ The Mapping Server advertises the SID mappings for the non-SR routers § for example, it advertises that Z is 16066
§ A and B install a normal SR prefix segment for 16066
§ C realizes that its next hop along the SPT to Z is not SR capable hence C installs an SR-to-LDP FIB entry § incoming label: prefix-SID bound to Z (16066) § outgoing label: LDP binding from D for FEC Z
§ A sends a frame to Z with a single label: 16066
LDP/SR Interworking - Mapping Server
A
C B D
Z Z(16066)
Input Label (SID)
Out Label (LDP), Interface
16066 16, 1
Prefix Out Label (SID), Interface
Z 16066, 0
SR LDP
Lab Testbed Topology (Mapping Server)
g0/0/0/1
g0/0/0/1
g0/0/0/0
g0/0/0/2
lo0
lo0
g0/0/0/0
lo0 lo0
IS-IS Area 49.0002
IS-IS Area 49.0001
LDP-Only LSR
SR Mapping Server
SR Mapping Server
SR Mapping Client
P1 IS-IS L1-L2
P2 IS-IS L1-L2
PE1 IS-IS L1
PE2 IS-IS L2
§ Leverages existing and proven LFA technology § P space - set of nodes reachable from node S (PLR) without using protected link L § Q space - set of nodes that can reach destination D without using protected link L
§ Enforcing loop-freeness on post-convergence path § Where can I release the packet?
At the intersection between the post-convergence shortest path and the Q space
§ How do I reach the release point? By chaining intermediate segments that are assessed to be loop-free
Topology Independent LFA – Implementation
1000
§ TI-LFA for link R1R2 on R1 § Calculate LFA(s)
§ Calculate post-convergence SPT
§ Find LFA on post-convergence SPT
§ R1 will steer the traffic towards LFA R5
TI-LFA – Zero-Segment Example
Packet to Z
Default metric:10
R5
R2 R1
A Z
R3
Packet to Z
R4
R5
Packet to Z
prefix-SID(Z)
§ TI-LFA for link R1R2 on R1 § Calculate P and Q spaces
§ They overlap in this case
§ Calculate post-convergence SPT § Find PQ node on post-
convergence SPT § R1 will push the prefix-SID of R4
on the backup path
TI-LFA – Single-Segment Example
Q-space
P-space
Packet to Z
prefix-SID(Z)
Packet to Z
Packet to Z
prefix-SID(Z)
prefix-SID(R4)
Default metric:10
R5
R2 R1
A Z
R3
Packet to Z
R4
§ TI-LFA for link R1R2 on R1 § Calculate P and Q spaces
§ Calculate post-convergence SPT
§ Find Q and adjacent P node on post-convergence SPT
§ R1 will push the prefix-SID of R4 and the adj-SID of R4-R3 link on the backup path
TI-LFA – Double-Segment Example
P-space Q-space
1000
Packet to Z
prefix-SID(Z)
Packet to Z
Packet to Z
prefix-SID(Z)
adj-SID(R4-R3)
prefix-SID(R4)
Packet to Z
prefix-SID(Z)
adj-SID(R4-R3) Default metric:10
R5
R2 R1
A Z
R3 R4 R3 R4
Packet to Z
g0/0/0/1 Metric=10 (default)
Testbed Topology (TI LFA)
g0/0/0/1
g0/0/0/0
g0/0/0/2
Metric=30
lo0
lo0
Metric=10 (default) g0/0/0/0
lo0
IS-IS Area 49.0002
IS-IS Area 49.0001
lo0
LDP-Only LSR
P1 IS-IS L1-L2
P2 IS-IS L1-L2
PE1 IS-IS L1
PE2 IS-IS L2
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